1. Field of the Invention
The present invention generally relates to insulators/conductors above copper wiring connections on exterior interconnection layers of an integrated circuit structure, and more particularly to an improved process and structure for forming such interconnection layers.
2. Description of the Related Art
Integrated circuit processing can be generally divided into front end of line (FEOL) and back and of line (BEOL) processes. During FEOL processing, the various logical and functional devices are manufactured. The FEOL processing will generally form many layers of logical and functional devices. Layers of interconnections are formed above these logical and functional layers during the BEOL processing to complete the integrated circuit structure. Therefore, BEOL processing generally involves the formation of insulators and conductive wiring and contacts.
Recently, insulators (dielectrics) that have a lower dielectric constant (and are softer) are replacing older, harder, higher dielectric constant insulators. Lower dielectric constant materials generally have a dielectric constant below 3.0 and include polymeric low K dielectrics commercial products such as SiLK, available from Dow Chemical Company, NY, USA, FLARE, available from Honeywell, NJ, USA, microporous glasses such as Nanoglass (Porous SiO2), available from Honeywell, Inc., NJ, USA, as well as Black Diamond (Carbon-doped SiO2), available from Applied Material, CA, USA; Coral (Silicon carbide based dielectrics), available from Novellus Systems, Inc., CA, USA; and Xerogel, available from Allied Signal, NJ, USA. These lower dielectric constant insulators are referred to as “low-K” dielectrics. These low-K dielectrics are advantageous because they decrease overall capacitance, which increases device speed and allows lower voltages to be utilized (making the device smaller and less expensive).
Metals (such as copper, tungsten, etc.) are generally used as wiring and electrical connections in the BEOL interconnection layers. One drawback of using low-K dielectrics in the BEOL interconnection layers is that the low-K dielectrics are more sensitive to metal migration (e.g., copper migration) than were the higher-K dielectrics. One conventional solution to this problem is to use a blanket dielectric cap (having a high dielectric constant) as a metal diffusion barrier for low K dielectric material above the metal features. This blanket dielectric cap also acts as an oxygen barrier to prevent oxygen in the low k dielectric material from oxidizing the metal.
However, this dielectric cap usually has higher dielectric constant and will greatly affect the effective dielectric constant of the overall dielectric material between metal features. In addition, the dielectric cap generally needs to have a minimum thickness (e.g., 250 A) to be effective. However, if the dielectric cap is formed above a certain thickness, it will substantially distort the dielectric constant of the interconnect layer above a desired level. Therefore, there is a need for a new type of interconnection layer that does not require a blanket dielectric cap. The invention described below provides a method and structure for creating such an interconnection layer.